Packaged microelectronic devices are used in cellular phones, pagers, personal digital assistants, computers, and many other electronic products. Conventional packaged microelectronic devices can include a singulated microelectronic die, an interposer substrate or lead frame attached to the die, and a molded casing around the die. The die generally includes an integrated circuit and an active side with a plurality of bond-pads coupled to the integrated circuit. The bond-pads are typically coupled to terminals on the interposer substrate or lead frame, and supply voltage, signals, etc., are transmitted to and from the integrated circuit via the bond-pads. In addition to the terminals, the interposer substrate can also include ball-pads coupled to the terminals by conductive traces supported in a dielectric material. Solder balls can be attached to the ball-pads in one-to-one correspondence to define a “ball-grid array.” Packaged microelectronic devices with ball-grid arrays are generally higher grade packages having lower profiles and higher pin counts than conventional packages using lead frames.
One such conventional packaged microelectronic device is a build up package (“BUP”) microelectronic device. BUP devices are formed by placing multiple singulated microelectronic dies active side down on a temporary carrier. A fill material is used to cover the dies and the carrier. Once the fill material sets up, the temporary carrier is removed. The active sides of the dies are cleaned and then a redistribution layer is applied to the active sides of the dies. Often solder balls are connected to the redistribution layer and a dielectric layer is placed over portions of the redistribution layer so that the solder balls extend through the dielectric layer. The fill material between the dies is then cut to separate the dies from one another and form multiple BUP devices. The solder balls and redistribution layer can then be used to connect the BUP device to a printed circuit board. In certain cases, the redistribution layer can extend beyond the edge of the die onto the fill material to increase the area available for the array of solder balls.
BUP microelectronic devices can also be formed by placing multiple singulated dies active side up on a temporary carrier and placing a fill material between the dies. Once the fill material hardens, the temporary carrier is removed and the BUP devices are separated by cutting the fill material between the dies. However, with this process it can be difficult to place a redistribution layer on the active sides because the active sides and the fill material between the dies may not form a sufficiently planar surface for effective and efficient application of a redistribution layer.
The foregoing processes have a large number of steps, and thus fabricating BUP devices can be time consuming and expensive. Additionally, BUP devices may not be well suited for use in stacked die arrangements because BUP devices generally only have contacts on the active side of each device. Accordingly, a significant amount of space on a circuit board must be reserved for BUP devices in products that require several such devices. This can be problematic because the sizes of electronic products that use BUP devices are decreasing in response to consumer demand. Therefore, it would be desirable to produce BUP devices that are well suited for stacked die arrangements.